Final working version and thanks kepstin on IRC Freenode, channel : ffmpeg.  This is a Boomerang effect.

ffmpeg -i MVI_6551.MOV -filter_complex \
"[0:v]trim=36:39, crop=720:720:540:0, setpts=PTS-STARTPTS, setpts=.8*PTS, loop=loop=0, split=2 [v1] [reverseMe]; \
 [reverseMe] reverse,setpts=PTS-STARTPTS, setpts=.8*PTS, loop=loop=0 [reverseVideo]; \

 [v1][reverseVideo] concat=n=2:v=1,split[n1][n2];[n1]palettegen[p];[n2][p]paletteuse [v]\

 " -map "[v]" -y o6.gif